Hey C,
a really good base layer is a farmer John style wetsuit, like you probably used for the beginner course. then a drytop, which can be pricey, check mountain equipment co-op's gear swap page, sometimes people have equipment they've grown out of. The booties they have at Valhalla are good, and the last piece of advice is to buy a cold weather cap. These are neoprene or the MEC one which is okay is rubber with a fleece lining.
Happy Shopping;
Jim